The present invention relates generally to pressure contact connectors, and more particularly to a land grid array (xe2x80x9cLGAxe2x80x9d) connector that uses a plurality of wires as contacts that are held in a flexible body portion of the connector.
The electronics industry has seen a large growth in the past few years of reduced size electronic devices and appliances, such as laptop computers and the like. The industry is always seeking to reduce the size of these components and to increase their functionality and capability. Both aims are accomplished by increasing the density of circuits on components of the device. Although the number of circuits established on a chip or circuit board may be increased, care must be taken to ensure that a reliable interconnection is established between the high density component and another component of the device.
These high-density interconnections are used for microprocessor, ASIC and other types of chips and may also be used to provide a connector between two circuit boards. Ball Grid Array (xe2x80x9cBGAxe2x80x9d) packages have been used as high-density interconnections for these type applications. In BGA style packages, pads are formed in a substrate and small, spherical balls of solder are placed in contact with the pads. These balls are then heated to provide connections between the chip and another circuit board. However, these balls often exhibit poor circuit board compliance and mechanical properties in effecting contact between the chip and the opposing circuit board. They are not always suitable to overcome variations that may occur in the substrate printed circuit board. Additionally, once the balls are heated to provide solder connections, the chip cannot be easily removed to correct any defect in the soldering, without reworking all of the solder balls and reflowing the ball grid array to the printed circuit board in another attempt to provide a reliable connection. Thus, it can be appreciated that the use of a BGA solder package does not provide a separable device interface.
Land grid array (LGA) connectors have been developed for such applications and they provide circuit paths between the device and the circuit board involving the use of conductive leads, such as formed metal contacts, that are typically embedded in a rigid plastic substrate to connect lands, or pads on a printed circuit board to the solder balls, or lands, that may be formed on a chip or other device. These lands are formed in a particular pattern in opposition to the solder balls/lands of the component to which the connector is mated. These LGA connectors offer numerous advantages over BGA devices in that they provide to the circuit or system designer, a separable interface between the chip/chip package and a circuit board that BGA devices cannot provide because they are soldered to circuit boards to effect their connections. However, in LGA connectors, each conductive lead must exert a particular spring force that should be maintained in order to establish a reliable interconnection to a device. A clamping force must be exerted against a chip to retain it in contact with the connector. Chips having contacts in excess of 1000 contacts may require a contact force of well over a hundred pounds.
U.S. Pat. No. 4,998,885, issued Mar. 21, 1991 describes such a style of connector in which wires with ball-shaped end portions are embedded within an elastomeric pad. However, the elastomeric pad must be precisely scored to a controlled depth by a laser in the area between the wires in order to increase the flexibility of the wires and the ball-shaped end portions thereof. Cutting these lines too deep in the elastomeric pad presents a risk of weakening the elastomer that supports the wires and possibly create unreliable contacts, in that some of the wires may buckle and thereby not fulfill their individual resilient mating functions. This not only complicates the manufacture of, but also increases the cost of manufacture of such connectors
The present invention is therefore directed to an improved LGA connector and method of making the connector that overcomes the aforementioned disadvantages.
Accordingly, it is a general object of the present invention to provide an LGA connector having a flexible body portion that supports a plurality of resiliently deformable contacts arranged in a high-density pattern so as to ensure a reliable connection between the connector and an opposing component or device.
Another object of the present invention is to provide a high density LGA connector having a resilient body portion that is reinforced by a reinforcement layer interposed between two elastomeric layers, and a plurality of contacts disposed in an array within the body portion, the contacts having free ends that extend above opposing surfaces of the body portion.
Another object of the present invention is to provide a reliable, high density LGA connector having a resilient body portion that is reinforced by a fabric extent interposed between two elastomeric layers, and a plurality of contacts disposed in an array within the body portion, the contacts having free ends that extend above opposing surfaces of the body portion.
Still another object of the present invention is to provide an LGA connector wherein the connector has a flexible body portion that supports a plurality of conductive wire contacts formed as flexible loops, having free ends that extending past opposing sides of the connector body portion.
Yet still another object of the present invention is to provide a pressure-activated connector having a fabric substrate encapsulated within an elastomer, the connector having a plurality of thin, resilient contacts disposed on the fabric substrate in a predetermined array and extending through the substrate, the contacts being formed as thin filaments of wire folded upon themselves into a dual-strand loop, the contacts having free ends that extend on opposite sides of the substrate.
A still further object of the present invention is to provide a LGA connector for high density applications, wherein the connector includes a frame that encompasses a central body portion, the body portion including at least one elastomeric extent that is reinforced by a reinforcement member at least partially embedded therein, the connector having a plurality of conductive contacts disposed in an array within the body portion, the contacts being formed from thin, conductive wires that are inserted into the central body portion, the contacts being formed as open loops that define interconnected, redundant circuit paths for each contact.
Yet still another object of the present invention is to provide a pressure-activated connector having a flexible body portion that is supported by a connector frame member, the frame member extending around the flexible body portion and defining the perimeter of the connector, the connector having at least one recess formed therein that forms a partial receptacle for a chip or chip package, and the flexible body portion including an elastomeric extent presented on at least one surface of the body portion, the elastomeric extent being reinforced by a fabric extent to which the elastomeric extent is attached, both of the elastomeric extent and the fabric extent having similar dimensions so as to impart uniform characteristics to the body portion throughout its entire area, and the connector including a plurality of conductive contacts that are inserted into the body portion of the connector, the contacts including conductive wire lengths that are stitched into the body portion, while bent upon themselves to thereby form two, adjacent and redundant circuit paths extending through the connector body portion, the contacts having free ends that project outwardly on opposite sides of the body portion for contacting two different electronic components, the contacts being supported by the body portion at approximately the mid-sections thereof.
Yet another object of the present invention is to provide a method for making an improved LGA conductor including the steps of: forming a pliable connector body portion by capturing a reinforcement member within an elastomer, supporting it on a support member, passing a length of conductive wire through center of a hollow insertion tool, stitching the length of wire into the connector body portion by moving the insertion tool into and out of penetrating contact with the body portion, while further cutting the wire after each such insertion so as to deposit a conductive wire in the body portion that has at least one free end that projects above a surface of the connector body portion.
A further object of the present invention is to provide a pressure-activated connector having a flexible body portion held within a rigid frame, the connector having a plurality of contacts embedded in the body portion, the contacts being inserted in the body portion as a pair of interconnected strands of conductive wire formed as open loops, each open loop having two free ends that extend past exterior, opposing surfaces of the connector body portion, the free end portions being angled sideways in an offset pattern matching the pattern of an opposing circuit component, the angling of the wires increasing the contact lengths thereof and presenting a knife edge to contact pads of opposing components.
Still a further object of the present invention is to provide an improved LGA connector having a flexible connector body portion formed from an elastomer, the body portion being supported on a frame and containing a plurality of individual conductive contacts, the contacts being formed as wire loops to provide a pair of redundant, conductive circuit paths in the connector body portion, the body portion having a plurality of openings each of which receives a wire loop therein, the wires that form the loop extending through the body portion on opposite sides of a centerline of the opening.
The present invention accomplishes these and other objects by way of its unique and novel structure.
In one principal aspect of the present invention and as exemplified by one embodiment thereof, the connector includes a flexible connector body portion that is supported in a tight outer frame. The flexible connector body portion utilizes a reinforcement member as a substrate, and to which an elastomer is applied. As exemplified by a first embodiment of the invention, the elastomer is positioned on both surfaces of a fabric extent that is used as the reinforcement member so that it preferably fills the interstices of the fabric to elastomer provides a self-sealing support surface on both sides of the fabric extent while the fabric extent provides reinforcement to the elastomer. The manner in which the elastomer attaches to the fabric extent may be an encapsulation, a lamination or layering.
Conventional fabrics may be used for the fabric extent, such as those which a woven in a conventional manner having warps and wefts (or fills) interlaced together, either in a uniform or staggered pattern, and it is contemplated that even non-woven fabrics, such as felts and the like may be used for reinforcement, provided that the elastomer used may bond or otherwise attach itself to the fabric extent in a manner to intimately contact the fabric extent and provide a resilient body as the connector body portion.
Thin wires are arranged in the connector body portion in a predetermined array and are inserted into the fabric substrate by passing them through a needle and inserting the needle in and out of the substrate so as to xe2x80x9cstitchxe2x80x9d the wire contacts in place in the connector body portion. The wires are bent upon themselves so that a contact is formed and inserted into the connector body portion that has the form of an open loop. The elastomer has a consistency sufficiently resilient to grab and hold the wires as they are stitched through the connector body portion, and the fabric extent has a consistency sufficient to provide reinforcement or a measure of rigidity to the elastomer.
In an alternate embodiment of the invention, the elastomer may be applied to only one surface of the reinforcement member. In still another embodiment of the present invention, the reinforcement member may utilize a solid sheet of film, preferably a polymer film, and most preferably a polyimide film such as that sold by E. I. DuPont under the trade name xe2x80x9cKaptonxe2x80x9d. Such films have a desired durability and do not fray as fabrics may, and the holes for the wire contacts may be easily formed therein by a laser to xe2x80x9cburnxe2x80x9d them through the entire body portion of the connector.
In another principal aspect of the present invention, the contacts are formed by stitching pairs of wires into the substrate, the pairs being formed from single wire strands that are bent them upon themselves at one end thereof to form dual strand wire lengths, or open loops, with the strands having a bend formed therein at one end thereof, while having two ends of the wire spaced close together or adjacent one another at the other end of the contact, so that one free end of each contact preferably has a loop configuration while the other free end of the contact has the butt ends of two of the wire strands. The wires extend past the substrate in a predetermined distance sufficient to provide a plurality of resilient contact beams that flex under pressure of an opposing component, such as a chip, so that Hertzian contact occurs between the contacts and the opposing contact pads on the circuit board. The wires may be bent in a certain direction to define a deflection direction, rather than relying upon buckling of the wires to provide the movement under deflection. The dual nature of the wire strands, whether they have a circular or rectangular/square cross-section, provide each contact of the connector with redundant circuit paths.
In still another principal aspect of the present invention, a length of each wire is passed through the center of an insertion tool that takes the form of a hollow needle, or tube, and bent upon itself to form a loop prior to the needle making an insertion stroke through the connector body portion. The insertion tool is then withdrawn, leaving a double strand wire held in the connector body portion at approximately the mid-section of the strands so that the free ends of the contacts extend past the two opposite surfaces of the connector body portion for approximately the same length. At a preselected distance in the removal of the insertion tool, the wires are cut to form a dual strand, free end of the connector contact, so that a pair of conductive paths are established for each contact in a single insertion and removal stroke of the insertion tool, thereby providing the connector with redundancy and lower inductance.
In yet still another principal aspect of the present invention, the insertion tool is provided with a tip being formed so that the wire may exit from the center of the tool but from the side of the tip. This tool may have an angled tip with a single point, or it may have multiple points that are aligned with each other in order to balance the insertion force on the tool as it penetrates the elastomer and, if present, its reinforcement member.
In yet another principal aspect of the present invention, a plurality of holes may be formed in connector body such as by cutting them with a laser, or pre-punching the body portion to form the holes. Once formed, the contacts are inserted into the holes.
These and other objects, features and advantages of the present invention will be clearly understood through consideration of the following detailed description.